Low Testosterone: How Do You Know When Levels Are Too Low?

In recent years, Spyros Mezitis, MD, PhD, has found himself talking to a lot more male patients about low testosterone, a diagnosis he says is becoming increasingly common.

"More men are getting older, and men are more open about talking about erectile dysfunction," Mezitis, an endocrinologist at Lenox Hill Hospital in New York City, tells WebMD.

On the one hand, increased diagnosis of low testosterone is driven by an aging population, less stigma, and more precise tests. But there's another big reason why men come to Mezitis' office for a testosterone test.

They come in saying they feel excessively fatigued, weaker, depressed, and that they have lost their sex drive -- all common symptoms of a drop in testosterone.

"As an endocrinologist, I'm thinking hormones," says Mezitis, who estimates that about a quarter to a third of the men he tests for low testosterone have levels below normal. "Sometimes it is testosterone, sometimes it is the thyroid, and sometimes it's something unrelated to hormones."

What Is Testosterone and Why Does It Decline?

Testosterone is a hormone. It's what puts hair on a man's chest. It's the force behind his sex drive.

During puberty, testosterone helps build a man's muscles, deepens his voice, and boosts the size of his penis and testes. In adulthood, it keeps a man's muscles and bones strong and maintains his interest in sex. In short, it's what makes a man a man (at least physically).

After age 30, most men begin to experience a gradual decline in testosterone. A decrease in sex drive sometimes accompanies the drop in testosterone, leading many men to mistakenly believe that their loss of interest in sex is simply due to getting older.

"Some say it's just a part of aging, but that's a misconception," says Jason Hedges, MD, PhD, a urologist at Oregon Health and Science University in Portland. A gradual decline in testosterone can't explain a near-total lack of interest in sex, for example. And for Hedges' patients who are in their 20s, 30s, and early 40s and having erectile problems, other health problems may be a bigger issue than aging.

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"A lot of the symptoms are mirrored by other medical problems," Hedges says. "And for a long time, we were not attributing them to low testosterone, but to diabetes, depression, high blood pressure, and coronary artery disease. But awareness and appreciation of low testosterone has risen. We recognize now that low testosterone may be at the root of problems."

Doctors will want to rule out any such possible explanations for symptoms before blaming them on low testosterone. They will also want to order a specific blood test to determine a man's testosterone level.

Low Testosterone: How Low Is Too Low?

The bottom of a man's normal total testosterone range is about 300 nanograms per deciliter (ng/dL). The upper limit is about 800ng/dL depending on the lab. A lower-than-normal score on a blood test can be caused by a number of conditions, including:

Some medicines and genetic conditions can also lower a man's testosterone score. Aging does contribute to low scores. In some cases, the cause is unknown.

A low score does not always translate to symptoms, Mezitis says, "but we often find something that's off when we see scores of 200 or 100 ng/dL."

Hedges agrees and warns that even if a man does not have symptoms, he may be well advised to seek treatment. Low testosterone scores often lead to drops in bone density, meaning that bones become more fragile and increasingly prone to breaks.

"That's something I would want to have a conversation about," Hedges says. "Bone density issues are not always apparent."

Low Testosterone Treatment

Having a gradual decline in your testosterone level as you age is to be expected. Treatment is sometimes considered if you're experiencing symptoms related to low testosterone.

If a young man's low testosterone is a problem for a couple trying to get pregnant, gonadotropin injections may be an option in some cases. These are hormones that signal the body to produce more testosterone. This may increase the sperm count. Hedges also describes implantable testosterone pellets, a relatively new form of treatment in which several pellets are placed under the skin of the buttocks, where they release testosterone over the course of about three to four months. Injections and nasal gels may be other options for some men.

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What Are the Risks and Benefits of Testosterone Treatment?

"If their symptoms are truly due to low testosterone, patients tell me that within a few weeks they notice a significant difference, though sometimes it is not too dramatic," Hedges says. "Sex is better, depression is better -- you can see it directly and quickly."

There are also risks. Testosterone treatment can raise a man's red blood cell count as well as enlarge his breasts. It can also accelerate prostate growth. Men with breast cancer should not receive testosterone treatment.

Testosterone treatment usually is not advised for men with prostate cancer. Hedges says some of the associations between testosterone replacement therapy and prostate health are currently being challenged. In his practice, he does offer testosterone treatment to men who have been treated for prostate cancer.

"The take-home [message] is treatment is safe as long as you get careful monitoring," Hedges says. "If there are known issues, patients should be treated by a specialist."